LiDAR system implementing wavelength conversion

ABSTRACT

A wavelength converter for LiDAR systems, such as automotive LiDAR, is disclosed. Implementation of the wavelength converter in LiDAR systems makes possible generation and modulation of laser light in the silicon response region, conversion of the laser light to an eye-safe wavelength for emission and reflection from a target, and efficient conversion of the wavelength of the laser light to the silicon response region. The wavelength converter may implement a single-loop counter-propagating wavelength conversion scheme which provides both up-conversion and down-conversion of the signal within the same loop. The wavelength conversion design also has the potential for vehicle-to-vehicle (V2V) communication to enable a combined LiDAR and V2V communication system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present non-provisional patent application claims the benefit of andpriority to U.S. Provisional Patent Application No. 63/113,363, filedNov. 13, 2020, the entire contents of which are incorporated herein byreference.

FIELD OF INVENTION

The present invention relates to light detection and ranging (“LiDAR”)systems and methods. In particular, the present invention relates towavelength conversion of a LiDAR signal, and in particular a lasersignal used in automotive LiDAR systems. The present invention alsorelates to vehicle-to-vehicle (V2V) communications. The presentinvention further relates to a system that fuses data from LiDAR and V2Vcommunication systems.

BACKGROUND OF THE INVENTION

A LiDAR system generally includes a transmitter and a receiver. Thetransmitter generates and modulates laser light and emits it forreflection from a target. At least part of the laser light that reflectsfrom the target is returned to the receiver of the LiDAR system. Thereceiver includes a detector and a LiDAR sensor. The detector detectsthe received laser light and directs it to the LiDAR sensor which,together with associated electronics, determines the distance to theobject based on the amount of time it took the laser pulse to travel toand return from the object or the frequency shift in the reflectionprocess.

An important issue in a LiDAR system is what wavelength to use for thelaser light. The current state of the art has two major competingwavelength regions for use in high-volume LiDAR applications, such asautomotive LiDAR systems. One wavelength region runs from the visiblespectrum up to about 1 μm. Many LiDAR systems in this wavelength regionoperate at a wavelength of 905 nm. One major company has a LiDAR systemat 850 nm. Other wavelengths are also used, but the use of this band ofwavelengths is determined by the easy detection of this band ofwavelengths by silicon detectors. This wavelength region usually usesinexpensive diode lasers that match the band of the receivers. Forexample, 905 nm laser diodes are inexpensive and are readily available.Thus, the major benefit of this wavelength region is lower cost and, notsurprisingly, a significant majority of the automotive LiDAR companiesoperate in this band of wavelengths.

However, the major disadvantage of this wavelength region is that it isin a spectral band that does not allow for high flux levels hitting thehuman eye. Laser eye damage is a major design constraint for manyautomotive LiDAR companies. As shown in FIG. 1 (which is reproduced frompage 15 of LiDAR Technologies and Applications by Dr. Paul McManamon,published in 2019), the allowed laser flux (power per unit area) isapproximately 1,000,000 times higher at a wavelength 1550 nm than it isat a wavelength 905 nm for nanosecond-pulse-width lasers. The ambientnoise due to solar spectral irradiance is smaller at 1550 nm bandcompared to 905 and 850 nm bands.

The other major competing wavelength region for high-volume LiDARapplications is in the region of 1550 nm. Longer range high-volumeLiDARs tend to use this wavelength because of the high laser energy thatit allows. The major disadvantage of this wavelength region is the needto use detectors that can respond to this wavelength, such as InGaAs.While some automotive LiDAR companies can keep the cost of the detectorsdown by only using single detectors, this approach does limit the designspace.

Currently, at least 80% of automotive LiDAR systems operate in theshorter wavelength (e.g., 905 nm) regime. There are limited options toincrease the range of a LiDAR system operating at this wavelength whilemaintaining eye safety. One of the best options currently available isto increase the laser aperture size. Increasing the aperture sizespreads out the laser power on transmit, and captures more light onreceive, thereby allowing lower laser flux with increased peak laserpower. However, increasing the laser aperture increases the size andweight of the LiDAR system.

There is, therefore, a need for an apparatus and method that overcomesone or more of the above and other deficiencies, and that could allowthe majority of automotive LiDAR companies operating in the visible tonear 1 μm region to dramatically reduce their eye-safety constraintswithout making major changes to their LiDAR systems.

Vehicle-to-vehicle (V2V) communications involve sending and receivingsignal to and from neighboring vehicles to communicate information andto identify the neighboring vehicles. This will increase the line ofsight, enhance the detection and ranging, and potentially increase thesafety and reduce collision risks. V2V communications could be doneusing a GPS signal or using optical signals. Due to lower solarirradiance noise at 1550 nm compared to 905 and 850 nm, and due to thesame eye safety concerns, the optical V2V communications tend to operateat a 1550 nm band. As mentioned for the LiDAR application, the cost andcomplexity for 1550 nm makes it less undesirable. Accordingly, there isa need for a wavelength conversion system to enable the low-cost signalgeneration and detection at a 905 nm or 850 nm band and conversion to a1550 nm band for transmission to the surrounding environment or toneighboring vehicles. As both LiDAR and V2V systems increase safety anda wavelength conversion solves the above-mentioned issues for bothsystems, there is a need to design a compact and combined system forboth applications.

SUMMARY OF THE INVENTION

It has now been found that the above and related objects of the presentinvention are obtained in the form of several related aspects, includinggeneration and modulation of laser light in the silicon response region,conversion of the laser light to an eye-safe wavelength for emission andreflection from a target, and efficient conversion of the wavelength ofthe reflected laser light to the silicon response region. This may allowa LiDAR system to be built using lower cost silicon components whileemitting laser light in a wavelength region that is safer to the humaneye.

More particularly, the present invention relates to a LiDAR system. TheLiDAR system includes an emitter that emits laser light having a firstwavelength; a wavelength converter that converts the emitted laser lightfrom the first wavelength to a second wavelength before the laser lightis transmitted toward the target and, after reflected laser light isreceived from the target, converts the reflected laser light from thesecond wavelength to the first wavelength; and a detector that receivesthe reflected laser light having the first wavelength from thewavelength converter.

In at least one embodiment, the wavelength converter includes awavelength-conversion loop that converts the first wavelength to thesecond wavelength and converts the second wavelength to the firstwavelength, the wavelength-conversion loop comprising a firstwavelength-conversion medium and a second wavelength-conversion medium.

In at least one embodiment, the first wavelength-conversion mediumconverts the first wavelength to the second wavelength or converts thesecond wavelength to the first wavelength based on a direction that theemitted laser light or the reflected laser light travels through thefirst wavelength-conversion medium.

In at least one embodiment, the first wavelength-conversion medium maybe a non-linear medium.

In at least one embodiment, the first wavelength-conversion medium maybe periodically poled lithium niobate.

In at least one embodiment, the second wavelength-conversion mediumconverts the first wavelength to the second wavelength or converts thesecond wavelength to the first wavelength based on a direction that theemitted laser light or the reflected laser light travels through thesecond wavelength-conversion medium.

In at least one embodiment, the second wavelength-conversion medium maybe a non-linear medium.

In at least one embodiment, the second wavelength-conversion medium maybe periodically poled lithium niobate.

In at least one embodiment, the emitted laser light includes a firstpolarization component and a second polarization component, wherein boththe first polarization component and the second polarization componenthave the first wavelength; the first wavelength-conversion mediumconverts the first wavelength of the first polarization component to thesecond wavelength; and the second wavelength-conversion medium convertsthe first wavelength of the second polarization component to the secondwavelength.

In at least one embodiment, the reflected laser light includes a firstpolarization component and a second polarization component, wherein boththe first polarization component and the second polarization componenthave the second wavelength; the first wavelength-conversion mediumconverts the second wavelength of the first polarization component tothe first wavelength; and the second wavelength-conversion mediumconverts the second wavelength of the second polarization component tothe first wavelength.

In at least one embodiment, both the first wavelength and the secondwavelength are transmitted to the target.

In at least one embodiment, telecommunication information is transmittedalong with the LiDAR signal.

In at least one embodiment, wavelength converter includes a first port;a second port; and a wavelength-conversion medium coupled to the firstport and the second port; wherein: the first wavelength is received atthe first port is converted to the second wavelength by thewavelength-conversion medium and is provided to the second port; and thesecond wavelength is received at the second port and is converted to thefirst wavelength by the wavelength-conversion medium and is provided tothe first port.

In at least one embodiment, the wavelength-conversion medium convertsthe first wavelength to the second wavelength based on a direction thatthe emitted laser light travels through the wavelength-conversionmedium; and the wavelength-conversion medium converts the secondwavelength to the first wavelength based on a direction that thereflected laser light travels through the wavelength-conversion medium.

In at least one embodiment, the wavelength-conversion medium may be anon-linear medium.

In at least one embodiment, the wavelength-conversion medium may beperiodically poled lithium niobate.

In at least one embodiment, the detector may be a silicon detector.

In at least one embodiment, the first wavelength is in a wavelengthregion that runs from the visible spectrum up to about 1 μm.

In at least one embodiment, the first wavelength is about 905 nm.

In at least one embodiment, the second wavelength is about 1550 nm.

Although specific features, capabilities and advantages have beenenumerated above, various embodiments may include some, none, or all ofthe enumerated features, capabilities and advantages. These and othertechnical features, capabilities and advantages of the disclosed subjectmatter, along with the invention itself, will be more fully understoodafter a review of the following figures, detailed descriptions andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described withreference to the accompanying figures, wherein:

FIG. 1 is a graph of allowed laser flux for pulsed lasers.

FIG. 2 is a block diagram of elements of a LiDAR system in accordancewith the present invention.

FIG. 3 is showing a wavelength conversion scheme for a LiDAR system inaccordance with the present invention.

FIG. 4 illustrates an aspect of the wavelength conversion scheme shownin FIG. 3.

FIG. 5 shows a schematic diagram of an embodiment of a wavelengthconversion scheme in accordance with the present invention.

FIG. 5A illustrates an aspect of the wavelength conversion scheme shownin FIG. 5.

FIG. 5B shows a modification of the embodiment of the wavelengthconversion scheme shown in FIG. 5.

FIG. 6 shows a schematic diagram of an alternative embodiment of awavelength converter in accordance with the present invention.

FIG. 6A illustrates an aspect of the operation of the wavelengthconverter shown in FIG. 6.

FIG. 7 shows output signals provided by the embodiment of the wavelengthconversion scheme shown in FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 2 shows a block diagram of an embodiment of a LiDAR system 100 inaccordance with the present invention. LiDAR system 100 generallyincludes a transmitter 110 and a receiver 120. The transmitter 110generates and modulates laser light. Emitter 112 emits laser light 114having a wavelength λ₁ to wavelength converter 116, where it isconverted from wavelength λ₁ to wavelength λ₂. Converted laser light 118having wavelength λ₂ is then sent to target 122.

At least part of the laser light 118 that is reflected from target 122is returned to the wavelength converter 116, which converts it toreflected laser light 124 having a wavelength λ₁. The receiver 120includes a detector 124 and a sensor 128. The detector 124 detects thereflected laser light 124 and directs it to the sensor which, togetherwith associated electronics (not shown), determines the distance to thetarget 122 based on the amount of time it took the laser pulse to travelto and return from the object.

In an exemplary embodiment of the present invention, emitter 112 emitslaser light 114 having a wavelength λ₁ of 905 nm and wavelengthconverter 116 down-converts it to laser light 118 having a wavelength λ₂of 1550 nm. (“Down-conversion” refers to a process by which thefrequency of a signal is shifted down (i.e., decreased). In view of theinverse relationship between the frequency of an electromagnetic wavesignal and its wavelength, the wavelength of a down-converted signal isincreased.)

In an exemplary embodiment of the present invention, the detector 126 isa silicon detector and wavelength converter 116 up-converts thereflected laser light 118 to laser light 124 having a wavelength of 905nm. (“Up-conversion” refers to a process by which the frequency of asignal is shifted up (i.e., increased). In view of the inverserelationship between the frequency of an electromagnetic wave signal andits wavelength, the wavelength of an up-converted signal is decreased.)

As shown in FIG. 2, wavelength converter 116 must provide consecutivedown-conversion of emitted laser light 114 and up-conversion ofreflected laser light 118. FIG. 3 shows a single-loop,counter-propagating wavelength conversion scheme 300 implemented inwavelength converter 116 in accordance with embodiments of the presentinvention. Wavelength conversion is done using a wavelength convertingcomponent such as a non-linear medium. As is well known to those ofskill in the art, mixing a laser input signal and a pump laser signal ina non-linear medium, such as a PPLN waveguide, shifts the wavelength ofthe laser input signal to a different wavelength due to sum- anddifference-frequency generation. As shown in FIG. 3, wavelengthconversion scheme 300 uses two such non-linear media 314, 320, whichmakes it capable of converting dual-polarization signals. In preferredembodiments, one or both of non-linear media 314, 320 may be aperiodically poled lithium niobate (“PPLN”) waveguide.

The input signal 114 having a wavelength λ₁ (see FIG. 1) is provided toa wavelength conversion loop 304. If input signal 114 is asingle-polarization signal, then it may exit polarizationmultiplexer/demultiplexer 308 in either the clockwise orcounter-clockwise direction of loop 304. If clockwise, then wavelengthconverting component such as a PPLN 314 will convert the wavelength ofinput signal 114 from λ₁ to λ₂. If counter-clockwise, then wavelengthconverting component 320 will convert the wavelength of input signal 114from λ₁ to λ₂. In either event, the signal 118 having a wavelength λ₂ isprovided at an output of a processing unit 318 (e.g., a polarizationmultiplexer/demultiplexer) and is sent to target 122.

If input signal 114 is a dual-polarization signal, polarizationmultiplexer/demultiplexer 308 separates the input signal 114 into afirst polarization component 310 and a second polarization component312. The first polarization component 310 travels clockwise aroundwavelength conversion loop 304 and is provided to wavelength convertingcomponent 314. Wavelength converting component 314 converts thewavelength of the first polarization component 310 from λ₁ to λ₂ andprovides a converted first polarization component 316 to a polarizationmultiplexer/demultiplexer 318. Similarly, the second polarizationcomponent 312 travels counter-clockwise around loop 304 and is providedto wavelength converting component 320. Wavelength converting component320 converts the wavelength of the second polarization component 312from λ₁ to λ₂ and provides a converted second polarization component 322to processing unit 318.

The converted first and second polarization components 316, 322 arecombined in processing unit 318 into signal 118 having a wavelength λ₂.Signal 118 is then sent to target 122.

Wavelength conversion loop 304 is also used to convert laser signal 118having wavelength λ₂ to laser signal 124 having wavelength λ₁. If lasersignal 118 is a single-polarization signal, then it may proceed toeither wavelength converting component 320 or wavelength convertingcomponent 314 after it exits polarization multiplexer/demultiplexer 318.Thus, either wavelength converting component 314 or wavelengthconverting component 320 will convert laser signal 118 having wavelengthλ₂ to laser signal 124 having wavelength λ₁. In either event, lasersignal 124 having a wavelength λ₁ exits wavelength conversion loop 304through polarization multiplexer/demultiplexer 308 and is provided todetector 126.

If laser signal 118 is a dual-polarization signal, when laser signal 118is returned to polarization multiplexer/demultiplexer 318, polarizationmultiplexer/demultiplexer 318 separates it back into converted first andsecond polarization components 316, 322. Converted first polarizationcomponent 316 is then provided to wavelength converting component 320,which converts the wavelength of converted first polarization component316 from λ₂ back to λ₁, thereby restoring original first polarizationcomponent 310. Similarly, converted second polarization component 322 isthen provided to wavelength converting component 314, which converts thewavelength of converted second polarization component 322 from λ₂ backto λ₁, thereby restoring original second polarization component 312.Both first and second polarization components 310, 312 then completetheir respective trips around wavelength conversion loop 304 and arere-combined in polarization multiplexer/demultiplexer 308 to providelaser signal 124 having wavelength λ₁. Laser signal 124 exits wavelengthconversion loop 304 through a polarization multiplexer/demultiplexer,such as polarizing beam splitter/combiner 308, and is provided todetector 126.

In the single-loop wavelength conversion scheme shown in FIG. 3, eachone of wavelength converting component 314, 320 provides bothup-conversion and down-conversion of the polarization components thatpass through it, depending upon the direction in which the polarizationcomponent passes through the wavelength converting component. Asdescribed in connection with FIG. 3, and as shown in FIG. 4, whenconverted first polarization component 316 passes through wavelengthconverting component 320 in a clockwise direction after leavingpolarization multiplexer/demultiplexer 318, wavelength convertingcomponent 320 up-converts first polarization component 316 from awavelength λ₂ (e.g., 1550 nm) to a wavelength λ₁ (e.g., 905 nm). Incontrast, when second polarization component 312 passes throughwavelength converting component 320 in a counter-clockwise directionafter leaving polarization multiplexer/demultiplexer 308, wavelengthconverting component 320 down-converts second polarization component 312from a wavelength λ₁ (e.g., 905 nm) to a wavelength λ₂ (e.g., 1550 nm).

Similarly, when first polarization component 310 passes throughwavelength converting component 314 in a clockwise direction afterleaving polarization multiplexer/demultiplexer 308, wavelengthconverting component 314 down-converts first polarization component 310from a wavelength λ₁ (e.g., 905 nm) to a wavelength λ₂ (e.g., 1550 nm).In contrast, when converted second polarization component 322 passesthrough wavelength converting component 314 in a counter-clockwisedirection after leaving polarization multiplexer/demultiplexer 318,wavelength converting component 314 up-converts second polarizationcomponent 322 from a wavelength λ₂ (e.g., 1550 nm) to a wavelength λ₁(e.g., 905 nm).

FIG. 5 shows an alternative embodiment of wavelength converter 116 usinga wavelength conversion scheme 500. Laser signal 114 (see FIG. 1) havinga wavelength λ₁ is provided to a wavelength conversion loop 504 througha circulator 506. If input signal 114 is a single-polarization signal,then it may exit polarization multiplexer/demultiplexer 508 in eitherthe clockwise or counter-clockwise direction of loop 504. If clockwise,then wavelength converting component 514 will convert the wavelength ofinput signal 114 from λ₁ to λ₂. If counter-clockwise, then wavelengthconverting component 530 will convert the wavelength of input signal 114from λ₁ to λ₂. In either event, the laser signal 118 having a wavelengthλ₂ is provided at an output of polarization multiplexer/demultiplexer526 and is sent to target 122.

If input signal 114 is a dual-polarization signal, polarizationmultiplexer/demultiplexer 508 separates the laser signal 114 into afirst polarization component 510 and a second polarization component512. The first polarization component 510 travels clockwise aroundwavelength conversion loop 504 and is provided to wavelength convertingcomponent 514 through an optional polarization controller 516 and awavelength-division multiplexer 518 (if needed). Polarization controller516 can be used to eliminate possible crosstalk between the first andsecond polarization components 510, 512. The wavelength conversion inwavelength converting component 514 is based on the sum- anddifference-frequency generation in wavelength converting component 514using a pump laser 520 (if needed). The pump laser 520 is provided towavelength converting component 514 through a beam splitter 522 andwavelength-division multiplexer 518 (if needed). Wavelength convertingcomponent 514 converts the wavelength of the first polarizationcomponent 510 from λ₁ to λ₂ and provides a converted first polarizationcomponent 524 to a polarization multiplexer/demultiplexer 526 throughwavelength-division multiplexer 528.

Similarly, the second polarization component 512 travelscounter-clockwise around loop 504 and is provided to wavelengthconverting component 530 through a wavelength-division multiplexer 538(if needed). The wavelength conversion in wavelength convertingcomponent 530 is based on the sum- and difference-frequency generationin wavelength converting component 530 using pump laser 520, which isprovided to wavelength converting component 530 through a beam splitter522 and wavelength-division multiplexer 538. Wavelength convertingcomponent 530 converts the wavelength of the second polarizationcomponent 512 from λ₁ to λ₂ and provides a converted second polarizationcomponent 532 to polarization multiplexer/demultiplexer 526 throughwavelength-division multiplexer 534.

The converted first and second polarization components 524, 532 arecombined in polarization multiplexer/demultiplexer 526 into an outputsignal 118 having a wavelength λ₂. Optical signal 118 having wavelengthλ₂ is then sent to target 122.

Wavelength conversion loop 504 is also used to convert laser signal 118having wavelength λ₂ to laser signal 124 having wavelength λ₁. If lasersignal 118 is a single-polarization signal, then it may proceed toeither wavelength converting component 530 or wavelength convertingcomponent 514 after it exits polarization multiplexer/demultiplexer 526.Thus, either wavelength converting component 514 or wavelengthconverting component 530 will convert laser signal 118 having wavelengthλ₂ to laser signal 124 having wavelength λ₁. In either event, lasersignal 124 having a wavelength λ₁ exits wavelength conversion loop 504through polarization multiplexer/demultiplexer 508 and is provided todetector 126 via an output of circulator 506.

If laser signal 118 is a dual-polarization signal, when laser signal 118is returned to polarization multiplexer/demultiplexer 526, polarizationmultiplexer/demultiplexer 526 separates it back into converted first andsecond polarization components 524, 532. Converted first polarizationcomponent 524 is then provided to wavelength converting component 530through wavelength-division multiplexer 534, which converts thewavelength of converted first polarization component 524 from λ₂ back toλ₁, thereby restoring original first polarization component 510. Thiswavelength conversion in wavelength converting component 530 is based onthe sum- and difference-frequency generation in PPLN 530 using pumplaser 520, which is provided to wavelength converting component 530through a beam splitter 522 and wavelength-division multiplexer 534.

Similarly, converted second polarization component 532 is then providedto wavelength converting component 514 through wavelength-divisionmultiplexer 528, which converts the wavelength of converted secondpolarization component 532 from λ₂ back to λ₁, thereby restoringoriginal second polarization component 512. This wavelength conversionin wavelength converting component 514 is based on the sum- anddifference-frequency generation in wavelength converting component 514using pump laser 520, which is provided to wavelength convertingcomponent 514 through a beam splitter 522 and wavelength-divisionmultiplexer 528.

Both first and second polarization components 510, 512 then completetheir respective trips around wavelength conversion loop 504 and arere-combined in polarization multiplexer/demultiplexer 508 to providelaser signal 124 having wavelength λ₁. Laser signal 124 exits wavelengthconversion loop 504 through polarization multiplexer/demultiplexer 508and is provided to detector 126 via an output of circulator 506.

To aid in understanding the operation of wavelength conversion loop 504,FIG. 5A shows the circulation of first polarization component 510 in aclockwise direction around wavelength conversion loop 504 using numberedarrows 1-14. Numbered arrows 1-4 and 11-14 indicate the portions ofwavelength conversion loop 504 where first polarization component 510has a wavelength λ₁. Numbered arrows 5-10 indicate the portions ofwavelength conversion loop 504 where first polarization component 510has a wavelength λ₂. As shown in FIG. 5A, these portions are the“inside” portions of wavelength conversion loop 504 (i.e., betweenwavelength converting components 514, 530).

It should be understood that reversing the directions of numbered arrows1-14 in FIG. 5A would show the circulation of second polarizationcomponent 512 in a counter-clockwise direction around wavelengthconversion loop 504. Numbered arrows 1-4 and 11-14 would indicate theportions of wavelength conversion loop 504 where second polarizationcomponent 512 has a wavelength λ₁. Numbered arrows 5-10 would indicatethe portions of wavelength conversion loop 504 where second polarizationcomponent 512 has a wavelength λ₂.

The wavelength conversion scheme 500 can be implemented using opticalfibers, including as appropriate single mode fibers, multimode fibers,and polarization-maintaining fibers. The wavelength conversion scheme500 can be implemented based on commercially available opticalcomponents.

In accordance with an embodiment of the present invention, the inputsignal 114 can have a wavelength λ₁ of 905 nm or 850 nm. In accordancewith another embodiment of the present invention, the laser signal 118at polarization multiplexer/demultiplexer 526 can have a wavelength λ₂of 1550 nm.

A well-known method to perform wavelength conversion is to use anonlinear process. In this case, usually, a pump laser is needed, andthe wavelength conversion medium could be a nonlinear crystal and anyform of a nonlinear medium. In some of the nonlinear process, the pumplaser 520 is undepleted. In view of this fact, in accordance withanother embodiment in accordance with the present invention, thewavelength conversion scheme 500 can employ a pump recycling whichrecirculates residual pump power from one nonlinear conversion medium tobe used in another one (or in the same wavelength conversion component).As shown in FIG. 5B, in the wavelength conversion scheme 500, pumprecycling can be implemented by connecting wavelength-divisionmultiplexers 528, 534 to one another via connection 540. In alternativeembodiments, pump recycling can be implemented using a highly reflectivecoating inside each wavelength conversion component 514, 530.

Another embodiment of wavelength converter 116 using a waveformconversion scheme 600 in accordance with the present invention is shownin FIG. 6.

Laser signal 114 (see FIG. 1) having a wavelength λ₁ is provided topolarization multiplexer/demultiplexer 606. If input signal 114 is asingle-polarization signal, then it may exit polarizationmultiplexer/demultiplexer 606 and proceed to wavelength convertingcomponent 612 through either wavelength-division multiplexer 614 orwavelength-division multiplexer 622. In either event, wavelengthconverting component 612 converts the laser signal 114 having wavelengthλ₁ to laser signal 118 having a wavelength λ₂. Laser signal 118 is thenprovided to polarization multiplexer/demultiplexer 620 through the otherwavelength-division multiplexer and is sent to target 122.

If the signal 114 is a dual-polarization signal, polarizationmultiplexer/demultiplexer 606 separates the laser signal 114 into afirst polarization component 608 and a second polarization component610. The first polarization component 608 is provided to wavelengthconverting component 612 through wavelength-division multiplexer 614.Pump laser 616 is also provided to wavelength converting component 612through wavelength-division multiplexer 614. Wavelength convertingcomponent 612 converts the wavelength of the first polarizationcomponent 608 from λ₁ to λ₂ and provides a converted first polarizationcomponent 618 to a polarization multiplexer/demultiplexer 620 throughwavelength-division multiplexer 622.

Similarly, the second polarization component 610 is provided towavelength converting component 612 through wavelength-divisionmultiplexer 622. Pump laser 624 is also provided to wavelengthconverting component 612 (if needed) through wavelength-divisionmultiplexer 622. Wavelength converting component 612 converts thewavelength of the second polarization component 610 from λ₁ to λ₂ andprovides a converted second polarization component 626 to polarizationmultiplexer/demultiplexer 620 through wavelength-division multiplexer614. The converted first and second polarization components 618, 626 arecombined in polarization multiplexer/demultiplexer 620 into laser signal118 having a wavelength λ₂. Laser signal 118 is then sent to target 122.

The operation of waveform conversion scheme 600 when laser signal 118having a wavelength λ₂ is converted to laser signal 124 havingwavelength λ₁ will now be described. Referring to FIG. 6A, laser signal118 having a wavelength λ₂ is provided to polarizationmultiplexer/demultiplexer 620. If laser signal 118 is asingle-polarization signal, then it may exit polarizationmultiplexer/demultiplexer 620 and proceed to wavelength convertingcomponent 612 through either wavelength-division multiplexer 614 orwavelength-division multiplexer 622. In either event, wavelengthconverting component 612 converts the laser signal 118 having wavelengthλ₂ to laser signal 124 having a wavelength λ₁. Laser signal 124 is thenprovided to polarization multiplexer/demultiplexer 606 through the otherwavelength-division multiplexer and is sent to detector 124.

If laser signal 118 is a dual-polarization signal, then polarizationmultiplexer/demultiplexer 620 separates the laser signal 118 into afirst polarization component 634 and a second polarization component636. The first polarization component 634 is provided to wavelengthconverting component 612 through wavelength-division multiplexer 622.Pump laser 624 is also provided to wavelength converting component 612through wavelength-division multiplexer 622. Wavelength convertingcomponent 612 converts the wavelength of the first polarizationcomponent 634 from λ₂ to λ₁ and provides a converted first polarizationcomponent 638 to polarization multiplexer/demultiplexer 606 throughwavelength-division multiplexer 614.

Similarly, the second polarization component 636 is provided towavelength converting component 612 through wavelength-divisionmultiplexer 614. Pump laser 616 is also provided to wavelengthconverting component 612 (if needed) through wavelength-divisionmultiplexer 614. Wavelength converting component 612 converts thewavelength of the second polarization component 636 from λ₂ to λ₁ andprovides a converted second polarization component 640 to polarizationmultiplexer/demultiplexer 606 through wavelength-division multiplexer622. The converted first and second polarization components 638, 640 arecombined in polarization multiplexer/demultiplexer 606 into laser signal124 having a wavelength λ₁. Laser signal 124 is then provided todetector 126.

As described above, a signal having a wavelength λ₂ coming from thesecond port of waveform correction scheme 600 will be converted towavelength λ₁ in its first port. Thus, waveform correction scheme 600works for both wavelengths λ₁ and λ₂ as the input wavelength. If theinput wavelength is λ₁, then the output wavelength will be λ₂, and viceversa. Waveform correction scheme 600 can work for both single anddouble-polarization signals. One main advantage of waveform correctionscheme 600 is its very fast response time.

FIG. 7 shows the constellation pattern provided by wavelength conversionscheme 500 of FIG. 5 for the consecutive up- and down-conversion ofdual-polarization QPSK data. The dual polarization QPSK data wasup-converted to a wavelength of 633 nm and consecutively down-convertedto a wavelength of 1560 nm. No delay compensation or any amplitudebalancing between the two polarizations of the QPSK data was needed.

The novel and inventive wavelength converter 116 in accordance withembodiments of the present invention provides several benefits andadvantages. The wavelength converter 116 has broadband applicationalthough it does not require broadband components. It works fromcontinuous-wave to high bit-rate signals since it has an almostinstantaneous response time. The wavelength converter 116 isphase-insensitive, which makes it suitable for phase-encoded signals. Italso does not matter what signal constellation (phase encoding) theinput signals use.

Wavelength converter 116 is further independent of the inputpolarization state and works for both single- and dual-polarizationsignals. In other words, any input signal (regardless of its propertiessuch as polarization, phase, temporal shape, and bitrate) will beconverted to another wavelength at the output while preserving theproperties of the input signal enabling using more of the spectrum wherecommercial hardware is not available.

The LiDAR signal sent to the target 122 can be tuned by using a tunablepump laser 520 while keeping the emitter and detector wavelengths 114and 124 fixed. The signal sent to the target λ₂ can be tuned to A whilethe λ₁ is fixed by only tuning the pump laser. This could be useful forexample if there is ambient noise at λ₂.

Since both up-conversion and down-conversion are performed in the sameloop, the wavelength converter 116 provides high environmental stability(e.g., reduces the effect of temperature fluctuations) and it reducesthe effects of amplitude noise (i.e., distortion) of the convertedsignal. Since both polarization components of a dual polarization signaltravel only in different directions within the same loop, polarizationmode dispersion (PMD) is minimized and there is no need to add adelay-line to compensate for PMD. Also, the counter-propagating schemein the same loop automatically results in a balanced wavelengthconversion for both polarizations and reduces the bit error rate penaltydue to an imbalance between the two orthogonal polarizations. Thisresolves the need to balance the two polarizations' amplitudes using apolarization-dependent optical attenuator.

The wavelength converter 116 in accordance with the embodiments of thepresent invention reduces complexity and cost. The single-loopcounter-propagating wavelength conversion scheme in accordance withembodiments of the present invention is less complex than conventionalwavelength conversion schemes and is less costly as it only uses two (oreven one) non-linear conversion devices (e.g., wavelength convertingcomponents) for wavelength conversion. The wavelength converter 116 inaccordance with embodiments of the present invention also enablesimplementation of all-optical wavelength conversion.

In accordance with an additional embodiment of the present invention, atelecommunication signal can be sent along with the LiDAR signal to thetarget 122. Due to the dual-polarization, phase-transparent, and fastresponse time of the wavelength conversion apparatus and methoddescribed in accordance with embodiments of the present invention, aphase-encoded, dual-polarization, and pulsed signal (all or anycombination of these encodings mentioned) can be wavelength convertedusing the same apparatus to carry information to target 122 and toreceive information from target 122. The received signal from target 122does not necessarily need to be reflected from target 122, but couldinstead be independently emitted from target 122. For example, thisapproach could be used for LiDAR and vehicle-to-vehicle (V2V)telecommunications.

In alternative embodiments in accordance with the present invention,both wavelengths λ₁ and λ₂ can be sent to the target 122. This could bedone using a residual λ₁ signal after the wavelength converter 116.Also, the wavelength converter 116 could be designed to have partialconversion efficiency.

Finally, due to residual pump recycling in optical embodiments inaccordance with the present invention, residual pump laser power fromone wavelength converting component can be used in another wavelengthconverting component (or in the same wavelength converting component),thereby reducing laser pump power consumption considerably and thusincreasing total power efficiency.

While this invention has been described in conjunction with exemplaryembodiments outlined above and illustrated in the drawings, it isevident that the principles of the present invention may be implementedusing any number of techniques, whether currently known or not, and manyalternatives, modifications and variations in form and detail will beapparent to those skilled in the art. Modifications, additions, oromissions may be made to the systems, apparatuses, and methods describedherein without departing from the scope of the present invention. Forexample, the components of the systems and apparatuses may be integratedor separated. Furthermore, the operations of the systems and apparatusesdisclosed herein may be performed by more, fewer, or other componentsand the methods described may include more, fewer, or other steps.Additionally, steps may be performed in any suitable order.

Accordingly, the exemplary embodiments of the invention, as set forthabove, are intended to be illustrative, not limiting, and the spirit andscope of the present invention are to be construed broadly and limitedonly by the appended claims, and not by the foregoing specification.

In addition, unless otherwise specifically noted, articles depicted inthe drawings are not necessarily drawn to scale.

What is claimed is:
 1. A LiDAR system, comprising: an emitter that emitslaser light having a first wavelength; a wavelength converter thatconverts the emitted laser light from the first wavelength to a secondwavelength before the laser light is transmitted toward the target and,after reflected laser light is received from the target, converts thereflected laser light from the second wavelength to the firstwavelength; and a detector that receives the reflected laser lighthaving the first wavelength from the wavelength converter; wherein: theemitted laser light comprises a first polarization component and asecond polarization component, wherein both the first polarizationcomponent and the second polarization component have the firstwavelength; the first wavelength-conversion medium converts the firstwavelength of the first polarization component to the second wavelength;and the second wavelength-conversion medium converts the firstwavelength of the second polarization component to the secondwavelength.
 2. A LiDAR system, comprising: an emitter that emits laserlight having a first wavelength; a wavelength converter that convertsthe emitted laser light from the first wavelength to a second wavelengthbefore the laser light is transmitted toward the target and, afterreflected laser light is received from the target, converts thereflected laser light from the second wavelength to the firstwavelength; and a detector that receives the reflected laser lighthaving the first wavelength from the wavelength converter; wherein: thereflected laser light comprises a first polarization component and asecond polarization component, wherein both the first polarizationcomponent and the second polarization component have the secondwavelength; the first wavelength-conversion medium converts the secondwavelength of the first polarization component to the first wavelength;and the second wavelength-conversion medium converts the secondwavelength of the second polarization component to the first wavelength.3. A LiDAR system, comprising: an emitter that emits laser light havinga first wavelength; a wavelength converter that converts the emittedlaser light from the first wavelength to a second wavelength before thelaser light is transmitted toward the target and, after reflected laserlight is received from the target, converts the reflected laser lightfrom the second wavelength to the first wavelength; and a detector thatreceives the reflected laser light having the first wavelength from thewavelength converter; wherein the wavelength converter comprises: afirst port; a second port; and a wavelength-conversion medium coupled tothe first port and the second port; wherein: the first wavelength isreceived at the first port and is converted to the second wavelength bythe wavelength-conversion medium and is provided to the second port; andthe second wavelength is received at the second port and is converted tothe first wavelength by the wavelength-conversion medium and is providedto the first port.
 4. The LiDAR system of claim 3, wherein: thewavelength-conversion medium converts the first wavelength to the secondwavelength based on a direction that the emitted laser light travelsthrough the wavelength-conversion medium; and the wavelength-conversionmedium converts the second wavelength to the first wavelength based on adirection that the reflected laser light travels through thewavelength-conversion medium.
 5. The LiDAR system of claim 3, whereinthe wavelength-conversion medium comprises a non-linear medium.
 6. TheLiDAR system of claim 5, wherein the wavelength-conversion mediumcomprises periodically poled lithium niobate.